Not applicable.
Prosthesis components for replacing large anatomical joints are well known in the art, including knee, shoulder, and ankle replacement systems. For example, knee replacement systems typically include femoral components that replace all or part of the joint surfaces of the end of the femur and tibial components that replace all or part of the upper surface of the tibia. The tibial component typically has two parts, a metal tray or shell that is affixed directly to the upper end of the tibia with bone screws, with cement, or with bone ingrowth into a porous undersurface of the tray, and a polymeric (e.g., polyethylene) liner secured within the tray. The lower end of the femoral component typically rounded lower end that simulates the condylar process of the femur. This condylar surface of the femoral component bears on the upper surface of the liner and permits articulation of the knee. The articulation of the femoral component on the polyethylene liner results in microscopic particles of polyethylene being worn from the liner. The metal trays typically have screw holes which receive bone screws that are anchored into the tibia to enhance immediate fixation. However, these screw holes can cause problems by allowing joint fluid along with the polyethylene debris to be forced into the screw holes under pressure and thus dissolve and destroy the bone structure supporting the tray. Even when occupied by a screw, the screw holes allow joint fluid and debris to migrate around the screw and to come into contact with the underlying bone structure, gradually loosening it and destroying bone.
Some efforts have been made to address these problems in the prior art. The polyethylene liner or component has been locked securely to the metal tray with a peripheral locking flange to prevent up and down motion of the polyethylene component and resultant high pressure pumping of joint fluid into the screw holes. These tight capture mechanisms do not, however, prevent joint fluid from bathing the screws, and in situations in which joint fluid pressure is elevated, such higher levels of joint fluid pressure can be transmitted to the screw holes, thus forcing joint fluid through the screw holes and into the bone proximate the screw holes and resulting in bone loss around screws and under empty screw holes. Over time, this loss of bone supporting the tray jeopardizes the structural integrity of the knee replacement system.
Another approach to minimizing the danger of bone loss is to minimize the wear on the under surface of the polyethylene component by polishing the metal tray. However, it has been found that most of the wear debris is generated at the actual bearing surface between the femoral and tibial joint surfaces, and is not affected by polishing the under surface of the polyethylene component.
Still another approach is to develop tibial trays with no screw holes. While this would eliminate the route of access of joint fluid and debris into the underlying bone, it eliminates the use of screws, which are a desirable or even necessary feature for fixation of the metal tibial tray onto the bone surface, particularly in patients with soft bone.
Reference may be made to my prior U.S. Pat. No. 5,766,260 entitled xe2x80x9cAcetabular Component With Improved Liner Seal and Lockxe2x80x9d, issued Jun. 16, 1998, which disclosed modular acetabular components in a total hip replacement system. In particular, my prior ""260 patent disclosed a continuous flexible seal on a part spherical plastic liner which sealingly engaged its part spherical metal shell for continuous 360xc2x0 sealing around the liner. More specifically, as the liner was installed in its acetabular shell, the liner would flex and would thus make a continuous seal with respect to the shell and a snap-lock securement was provided to secure the part-spherical liner within the part-spherical shell. This acetabular liner was fixedly secured to its shell by means of peripheral tabs on the liner which were received in corresponding notches in the shell, and by means of interlocking ridges extending around the part spherical shell which were received in a continuous interlocking groove on the inner face of the shell.
As reported in a paper entitled xe2x80x9cEffect of Locking Mechanism On Particle and Fluid Migration Through Modular Acetabular Componentsxe2x80x9d, by Cyna Kalily et al., presented at the 64th Annual Meeting of the American Academy of Orthopaedic Surgeons, Feb. 13-17, 1997, a seal, such as described in the above-noted ""260 patent, which was incorporated in the MicroSeal(copyright) hip system (similar to that described in my ""260 patent) commercially available from Whiteside Biomechanics, Inc., of St. Louis, Mo., was effective in preventing the migration of joint fluid and debris between the liner and the metal shell. Because the continuous seal of the MicroSeal(copyright) hip system prevented joint fluid from passing coming into contact with the bone structure under the tray, degeneration of bone structure proximate the bone screws anchoring the shell would be considerably lessened.
As noted above, it has been known that the migration of joint fluid and debris through the screw holes in a tibial tray in a total knee replacement system caused degeneration of the tibia supporting the tibial tray. However, in attempting to incorporate a continuous seal, such as disclosed in the ""260 patent, which was only used with a part spherical shell in a tibial tray in a knee replacement system, it was found that continuous peripheral tabs and corresponding continuous notches and the locking ridge/locking groove arrangement disclosed in the ""260 patent would not permit a surgeon to snap lock the liner into the tibial tray. This is due to the fact that in knee, ankle, shoulder and other large joint replacement systems, the liner component cannot be laid directly symmetrically on the metal shell (e.g., on the tray) component and pressed into place, as it can be in inserting a liner in an acetabular shell of a hip replacement system. Typically, the liners for such other joint replacement systems must be inserted from the front, side or back because of the presence of tissue, ligaments or the like. Because of the necessity of the front, side or back insertion of the liner into its tray, the surgeon oftentimes cannot apply a load directly to the center of the polymeric liner of sufficient magnitude to drive the liner into place within its tray or shell component. It has also been found that due to the difficultly of inserting such liners into their respective tray or shell components, the close tolerances required to prevent movement of the liner with respect to the tray during usage of the appliance by the patient could not be maintained.
In summary, there has been a long-standing need for a joint replacement component (e.g., a tibial tray) and liner which are of non-spherical or non-circular shape that effectively prevents the migration of joint fluid and debris from the tray to the bone structure receiving the bone screws which secure the tray to the tibia, which maintains the close tolerances needed to rigidly secure the liner within the tray to prevent relative movement, and yet which liner can be readily installed by the surgeon once the component (tray) has been affixed to the tibia.
Among the several objects and features of the present invention may be noted the provision of a joint replacement component, such as a non-part spherical tibial tray for a knee replacement system, and a non-part-spherical polymeric (polyethylene) liner having a continuous seal integrally formed on the liner and extending completely around the liner for continuously sealing the liner with respect to the tray thereby to prevent the migration of joint fluid and other debris (or contaminants) from the tray to the bone structure supporting the tray via bone screw holes in the tray which is easy for the surgeon to install and which is securely held in place where the liner may be readily snap-locked into place by the surgeon during the surgery;
The provision of such a joint replacement component, such as a tray, in which the liner is positively maintained within the tray such that the seating surfaces of the tray and the liner remain in their desired positions relative to one another even under alternating biomechanical loading during long term use;
The provision of a tibial tray for a knee replacement system which, during installation, allows the liner to be inserted from one side leaving ligaments and capsule in tact on the surfaces that have not been surgically transected;
The provision of such a joint replacement component which provides positive, tactile securement of the liner with the component during installation of the liner so as indicate to the surgeon of complete and proper seating of the liner;
The provision of such a joint replacement system in which the liner component is positively seated with respect to its tray or shell component so as to effectively prevent toggling, rocking, or slipping of the liner with respect to the tray component throughout a range of biomechanical loads and throughout a range of biomechanical movement of the components of the total knee (or other joint) replacement system over the service life of the total joint replacement system;
The provision of such a joint replacement system which minimizes the loss or destruction of the soft bone supporting the tray component due to exposure of the joint to joint fluid seeping or forced into contact with the bone structure via screw holes in the tray or shell component; and
The provision of such a joint replacement component which made of materials suitable for implantation, which is of simple and rugged construction, which requires minimal space when installed, which is easy and fast to install, and which has a long service life once installed.
A joint replacement component for a total joint replacement system of the present invention comprises a tray made of a suitable implantable metal. The tray has a base and a wall (or rim) extending upwardly from the base for defining a recess, the recess having a non-circular shape corresponding generally to the non-circular shape of the tray. The base has one or more holes therein for receiving bone fixation fasteners for fixation of the tray with respect to a suitable skeletal structure. A liner of suitable synthetic resin material is provided for securement within the recess after the tray has been surgically affixed to the tibia. The liner has a non-circular shape corresponding generally to the non-circular shape of the recess. The tray wall has an inner wall surface which substantially defines the outer periphery of the recess with the inner wall surface tapering inwardly and downwardly toward the base tray. The inner wall surface has an undercut groove on the opposite end or side of the recess. The liner has a side wall generally of the same non-circular shape as the tray wall and is sized with respect to the tray wall as to fit closely within the inner wall surface such that with the liner installed in the recess of the tray, the liner and the inner wall surface are dimensioned with respect to one another so that with the tray and the liner at body temperature, the liner is securely held within the recess by the tray wall thereby to substantially eliminate movement of the liner with respect to the tray upon subjecting the tibial component to biomechanical loads during normal use of the knee replacement system. The liner side wall has a continuous seal formed integrally with the liner with the seal sealingly engaging the inner wall surface when the liner is installed within the recess thereby to prevent the migration of joint fluid and/or debris past the seal into communication with the holes in the base of the tray. The liner further has at least one locking tab or flange on opposite ends or sides thereof. The locking tabs are preferably integral with the liner and are engageable with the undercut groove in the inner wall surface thereby to snap-lock the liner within the tray as the liner is inserted into the tray by a surgeon after the tray has been surgically affixed to the tibia.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.